Presently, a number of schemes exist to convert angular or linear mechanical position to a digital output. The most simple converters are potentiometers, which convert position to an output voltage by acting as a resistive divider. Their analog output can then be converted to a digital format, if required. In a case calling for an output signal that consists of discrete steps, a multiposition switch is the present choice.
With the advance of microprocessor-based equipment, digital incremental encoders have emerged. They typically employ a single track and two sensors arranged to produce a pair of square wave patterns with a 90.degree. phase shift. An up/down counter is connected to the sensor outputs to deliver position information. If a second track bearing an index marker is provided, the counter can be reset when the index position is sensed. Thus a quasi-absolute scheme results, in that accurate position information can be provided so long as power remains on, but after a power-up condition the position information is not accurate until a relative position is reached in which the index marker resets the counter.
Where true absolute information is required, for example where accurate position information is needed following a power-on condition without relative movement of the encoder parts, multitrack encoders are the most common choice. They typically feature a number of tracks equivalent to the .sup.2 log of the number of steps to be resolved, for example 8 tracks for a 256 step encoder. The aforementioned encoders most commonly utilize an optical scheme with a photographically fabricated coding wheel bearing a Gray code and LED/phototransistor combinations as detectors.
Other principles worth mentioning are inductive or capacitive resolvers. Both schemes are by nature analog; their two or three phase outputs can be digitized and the rotary angle computed from the respective signal amplitudes. Synchro resolvers are a good example of a three-phase inductive rotary encoder. An application for a linear encoder is found in digital calipers.
One object of the invention is to provide an encoding principle which can yield a digitized absolute angular or linear position.